The issue is, might_atomic says he is cynical that the reason the law is the case isn't dumb, it's intentional. If we're being cynical, I can think of many ways to be extra punitive against any particular drug you like for any reason. Even if we assume self-aggrandizement, my assumption was we could all be fall more cynically creative as to how a drug enforcement agency could get than arguing about the weight of paper.
For example, why not just call all the precursor chemicals drug as well, we could say they produced 50lbs of lsd because of the running water used in the process.
I'm just advocating for a level of cynicism that looks at a bigger picture to where once in awhile we could say something is dumber than it is insidious. Without doing so, I think it contributes to the persistence of laws that are in fact dumber than even their creators intended.